As a leading cause of disability and death worldwide, chronic obstructive pulmonary disease (COPD) is defined spirometrically, based solely on a reduced ratio of the forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC), with severity subsequently staged according to the FEV1, expressed as percent predicted (%Pred). Among older persons, current spirometric guidelines for COPD are problematic, however, for at least three reasons. First, the threshold that establishes a reduced FEV1/FVC remains controversial. Second, expressing the FEV1 as %Pred is seriously flawed, because it does not account for differences in the variability of the reference group across the lifespan. Third, current spirometric guidelines have not been rigorously validated using important clinical measures such as mortality and respiratory symptoms. In response, we have developed a two-part spirometric strategy for defining COPD that first determines a cut-point for the FEV1/FVC based on mortality risk;and then, among persons below this critical FEV1/FVC threshold, determines cut-points for the FEV1, expressed as a standardized residual percentile (SR-tile)- and based on mortality risk and respiratory symptoms. Importantly, the SR-tile method accounts for variability of the reference group. The objective of this R03 application is to validate our spirometric definition of COPD, relative to current guidelines, by using data from two large population-based studies of older persons: the Health, Aging and Body Composition Study and the Cardiovascular Health Study. Validation will be based on longitudinal associations with health-related outcomes, including hospitalizations and mortality, and on cross-sectional associations with clinical features, including respiratory symptoms, physical performance, and medication use. Our long-term goal is to evaluate the risk and host factors, as well as the mediators, that underlie the association between pulmonary function and health-related outcomes, in older persons. This R03 application is an important step because it will validate an age-appropriate method for reporting pulmonary function and for defining COPD. PUBLIC HEALTH RELEVANCE: Among older persons, current spirometric guidelines may lead to misclassification (mainly over- diagnosis) of COPD and, in turn, potentially compromise patient care. We propose to validate a more evidence-based spirometric strategy that will avoid the misidentification of COPD among older persons. This could lead to more judicious use of COPD-specific pharmacotherapy and, as a result, reduce the frequency of medication-related adverse events.